Re: [PATCH rc v6 3/7] iommu/arm-smmu-v3: Do not enable EVTQ/PRIQ interrupts in kdump kernel

[Pranjal Shrivastava <praan@google.com>]

On Wed, May 20, 2026 at 10:03:20AM -0700, Nicolin Chen wrote:
> In kdump cases, the crashed kernel's CDs and page tables can be corrupted,
> which could trigger event spamming. Also, we cannot serve page requests.
> 
> Skip the IRQ setup for EVTQ/PRIQ in arm_smmu_setup_irqs().
> 
> Skip their IRQ handler registration in unique-IRQ and combined-IRQ cases.
> 
> Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU is enabled in kdump kernel")
> Cc: stable@vger.kernel.org # v6.12+
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 58 ++++++++++++++-------
>  1 file changed, 39 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 2d7eb42449eaf..e00b28e36f9c4 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2464,7 +2464,11 @@ static irqreturn_t arm_smmu_combined_irq_thread(int irq, void *dev)
>  
>  static irqreturn_t arm_smmu_combined_irq_handler(int irq, void *dev)
>  {
> -	arm_smmu_gerror_handler(irq, dev);
> +	irqreturn_t ret = arm_smmu_gerror_handler(irq, dev);
> +
> +	/* In kdump, EVTQ/PRIQ are disabled and there is no thread to wake */
> +	if (is_kdump_kernel())
> +		return ret;
>  	return IRQ_WAKE_THREAD;
>  }
>  
> @@ -4963,6 +4967,21 @@ static void arm_smmu_setup_unique_irqs(struct arm_smmu_device *smmu)
>  	arm_smmu_setup_msis(smmu);
>  
>  	/* Request interrupt lines */
> +	irq = smmu->gerr_irq;
> +	if (irq) {
> +		ret = devm_request_irq(smmu->dev, irq, arm_smmu_gerror_handler,
> +				       0, "arm-smmu-v3-gerror", smmu);
> +		if (ret < 0)
> +			dev_warn(smmu->dev, "failed to enable gerror irq\n");
> +	} else {
> +		dev_warn(smmu->dev,
> +			 "no gerr irq - errors will not be reported!\n");
> +	}
> +
> +	/* No EVTQ/PRIQ interrupts in kdump -- queues are disabled */
> +	if (is_kdump_kernel())
> +		return;
> +
>  	irq = smmu->evtq.q.irq;
>  	if (irq) {
>  		ret = devm_request_threaded_irq(smmu->dev, irq, NULL,
> @@ -4975,16 +4994,6 @@ static void arm_smmu_setup_unique_irqs(struct arm_smmu_device *smmu)
>  		dev_warn(smmu->dev, "no evtq irq - events will not be reported!\n");
>  	}
>  
> -	irq = smmu->gerr_irq;
> -	if (irq) {
> -		ret = devm_request_irq(smmu->dev, irq, arm_smmu_gerror_handler,
> -				       0, "arm-smmu-v3-gerror", smmu);
> -		if (ret < 0)
> -			dev_warn(smmu->dev, "failed to enable gerror irq\n");
> -	} else {
> -		dev_warn(smmu->dev, "no gerr irq - errors will not be reported!\n");
> -	}
> -
>  	if (smmu->features & ARM_SMMU_FEAT_PRI) {
>  		irq = smmu->priq.q.irq;
>  		if (irq) {
> @@ -5005,7 +5014,7 @@ static void arm_smmu_setup_unique_irqs(struct arm_smmu_device *smmu)
>  static int arm_smmu_setup_irqs(struct arm_smmu_device *smmu)
>  {
>  	int ret, irq;
> -	u32 irqen_flags = IRQ_CTRL_EVTQ_IRQEN | IRQ_CTRL_GERROR_IRQEN;
> +	u32 irqen_flags = IRQ_CTRL_GERROR_IRQEN;
>  
>  	/* Disable IRQs first */
>  	ret = arm_smmu_write_reg_sync(smmu, 0, ARM_SMMU_IRQ_CTRL,
> @@ -5020,19 +5029,30 @@ static int arm_smmu_setup_irqs(struct arm_smmu_device *smmu)
>  		/*
>  		 * Cavium ThunderX2 implementation doesn't support unique irq
>  		 * lines. Use a single irq line for all the SMMUv3 interrupts.
> +		 *
> +		 * In kdump, EVTQ/PRIQ are disabled, so no threaded handling.
>  		 */
> -		ret = devm_request_threaded_irq(smmu->dev, irq,
> -					arm_smmu_combined_irq_handler,
> -					arm_smmu_combined_irq_thread,
> -					IRQF_ONESHOT,
> -					"arm-smmu-v3-combined-irq", smmu);
> +		if (is_kdump_kernel())
> +			ret = devm_request_irq(smmu->dev, irq,
> +					       arm_smmu_combined_irq_handler, 0,
> +					       "arm-smmu-v3-combined-irq",
> +					       smmu);

This `if` isn't needed, we can continue using devm_request_threaded_irq,
if you look at the doc for devm_request_threaded_irq [1] it says:

/**
 * devm_request_threaded_irq - allocate an interrupt line for a managed device with error logging
 * @dev:	Device to request interrupt for
 * @irq:	Interrupt line to allocate
 * @handler:	Function to be called when the interrupt occurs
 * @thread_fn:	Function to be called in a threaded interrupt context. NULL
 *		for devices which handle everything in @handler
 * @irqflags:	Interrupt type flags
 * @devname:	An ascii name for the claiming device, dev_name(dev) if NULL
 * @dev_id:	A cookie passed back to the handler function
[...]
*/

So, we can pass handler() here while leaving the thread_fn == NULL:

ret = devm_request_threaded_irq(smmu->dev, irq,
         arm_smmu_combined_irq_handler,
         is_kdump_kernel() ? NULL : arm_smmu_combined_irq_thread,
         IRQF_ONESHOT,
         "arm-smmu-v3-combined-irq", smmu);

(In fact that's exactly what devm_request_irq does under the hood [2])

Additionally, the arm_smmu_combined_irq_handler() returns 
IRQ_WAKE_THREAD unconditionally, which causes us to hit the warn_on[3] in
__handle_irq_event_percpu.

Hence, we'd need to refactor the arm_smmu_combined_irq_handler() to
return IRQ_HANDLED / _NONE if is_kdump_kernel().

> +		else
> +			ret = devm_request_threaded_irq(
> +				smmu->dev, irq, arm_smmu_combined_irq_handler,
> +				arm_smmu_combined_irq_thread, IRQF_ONESHOT,
> +				"arm-smmu-v3-combined-irq", smmu);
>  		if (ret < 0)
>  			dev_warn(smmu->dev, "failed to enable combined irq\n");
>  	} else
>  		arm_smmu_setup_unique_irqs(smmu);
>  
> -	if (smmu->features & ARM_SMMU_FEAT_PRI)
> -		irqen_flags |= IRQ_CTRL_PRIQ_IRQEN;
> +	/* No EVTQ/PRIQ IRQ generation in kdump -- queues are disabled */
> +	if (!is_kdump_kernel()) {
> +		irqen_flags |= IRQ_CTRL_EVTQ_IRQEN;
> +		if (smmu->features & ARM_SMMU_FEAT_PRI)
> +			irqen_flags |= IRQ_CTRL_PRIQ_IRQEN;
> +	}
>  
>  	/* Enable interrupt generation on the SMMU */
>  	ret = arm_smmu_write_reg_sync(smmu, irqen_flags,
> -- 
> 2.43.0
> 

Thanks,
Praan

[1] https://elixir.bootlin.com/linux/v7.1.1/source/kernel/irq/devres.c#L75
[2] https://elixir.bootlin.com/linux/v7.1.1/source/include/linux/interrupt.h#L218
[3] https://elixir.bootlin.com/linux/v7.1.1/source/kernel/irq/handle.c#L225